This invention relates to electrical systems and more particularly, to a system, and method, and computer software code for isolating electrical ground and secondary failures in electrical systems.
Electrical systems may sometimes encounter faults, such as AC grounds, DC grounds or impedances outside of acceptable ranges. When such faults occur, they may mildly or seriously damage the electrical system. Electrical systems are used in a vast variety of machines or components.
One such apparatus which uses a variety of electrical systems is a locomotive. A locomotive has a plurality of electrical systems on it. One such electrical system on a locomotive is a propulsion system. For example, a conventional diesel electric locomotive generally has a prime mover, typically a turbo-charged diesel engine with cylinders ranging from twelve to sixteen, to drive an electrical transmission. The electrical transmission generally comprises a synchronous generator that supplies electric current to a plurality of alternating current (AC) traction motors whose rotor are drivingly coupled through speed reducing gearing to respective axle wheel sets of the locomotive.
In one version, these locomotives will have an individual inverter connected to an individual traction motor while in other versions there may be multiple traction motors connected to a single inverter. The number of combinations of inverters/traction motors on a locomotive may vary also, such as from three to six, depending of the type or style of locomotive. The inverters and traction motors are used for propulsion and braking. Again, depending on the type of locomotive, there can be a plurality of parallel paths of dynamic braking grids or grid boxes, such as ranging from three to six parallel paths of dynamic braking grids. Each grid box can be either a series or parallel combination of resistances. The generator typically comprises a main three-phase traction alternator. When excitation current is supplied to field windings on the rotating rotor, alternating voltages are generated in three-phase armature windings on the stator of the alternator. These voltages are rectified to produce a controlled amplitude DC voltage and then applied to one or more of the inverters which control the effective frequency of alternating current to be supplied to the armature windings of the traction motors.
During dynamic braking, power comes from the traction motors. If there is not enough power from the traction motors, additional power is supplied from the alternator to the braking grids to maintain a proper DC link voltage to support traction motor excitation. At low speeds, when there is little power from the traction motors, most of the power is provided from the alternator during braking.
While in operation, electrical grounds, either an AC ground or DC ground, may develop in the propulsion circuit. An AC ground is a ground where the voltage at the ground fault point has a predominantly AC component with respect to the system grounding point. A DC ground is a ground where the voltage at the ground fault point has a predominantly DC component with respect to the ground. Thus as an illustration, in a DC locomotive, the system grounding point is typically at neutral point of the alternator. If the grounding point is the neutral of the alternator and if a ground on a DC bus exists, the ground may appear as an AC ground.
If not detected in time, this problem can severally damage components of the propulsion system. Additionally, impedance changes could occur which could also damage components of the propulsion system. Resistance changes occur because of either a short or an open circuit in a resistance. An open circuit in a portion of a resistor or a short circuit in a portion of a resistor, which would change the resistance, could damage additional components. Either certain components or the rest of the circuit may encounter a high power density or higher temperatures, thus damaging the electrical system.
Even though systems and techniques may exist today to effectively handle these problems, they do not necessarily apply less total power, less time in power, and less power for any components which are experiencing increased stress as a result of the original component failure. Furthermore, they do not all provide for a confirmation process to ensure isolation accuracy of failed components. They also do not provide for an early failure detection and handling based on specific operation information which may include comparison between similar devices.
Additionally, AC locomotives typically have from four (4) to six (6) parallel electrical paths for dynamic braking resistors. Any failure of these resistors and any associated circuits can cause extensive damage to the resistor system and other equipment if operation in a failed state continues for a sufficiently long time. Similar conditions exist in DC locomotives wherein they also may have 4 or 6 electrical paths for dynamic brake resistors. However they are connected independently.